The present invention relates to compositions and methods for enhancing the effect of vaccines in animals, such as domestic, sport, or pet species, and humans. More particularly, preferred embodiments concern the use of Ribavirin as an adjuvant and compositions having Ribavirin and an antigen.
The use of vaccines to prevent disease in humans, farm livestock, sports animals, and household pets is a common practice. Frequently, however, the antigen used in a vaccine is not sufficiently immunogenic to raise the antibody titre to levels that are sufficient to provide protection against subsequent challenge or to maintain the potential for mounting these levels over extended time periods. Further, many vaccines are altogether deficient in inducing cell-mediated immunity, which is a primary immune defense against bacterial and viral infection. A considerable amount of research is currently focussed on the development of more potent vaccines and ways to enhance the immunogenicity of antigen-containing preparations. (See e.g., U.S. Pat. Nos. 6,056,961; 6,060,068; 6,063,380; and Li et al., Science 288:2219-2222 (2000)).
Notorious among such xe2x80x9cweakxe2x80x9d vaccines are hepatitis B vaccines. For example, recombinant vaccines against hepatitis B virus such as Genhevacb (Pasteur Merieux Serums et Vaccines, 58, Avenue Leclerc 69007 Lyon, France), Engerixb (Smith, Kline and Symbol French), and Recombivaxhb (Merck, Sharp, and Dhome) are effective only after at least three injections at 0, 30, and 60 or 180 days, followed by an obligatory booster after one year. (Chedid et al., U.S. Pat. No. 6,063,380). Additionally, many subjects receiving these vaccines respond poorly, if at all. Because many regions of the world are endemic for HBV infection, the poorly immunogenic character of existing HBV vaccines has become an extremely serious problem.
To obtain a stronger, humoral and/or cellular response, it is common to administer a vaccine in a material that enhances the immune response of the patient to the antigen present in the vaccine. The most commonly used adjuvants for vaccine protocols are oil preparations and alum. (Chedid et al., U.S. Pat. No. 6,063,380). A greater repertoire of safe and effective adjuvants is needed.
Nucleoside analogs have been widely used in anti-viral therapies due to their capacity to reduce viral replication. (Hosoya et al., J. Inf. Dis., 168:641-646 (1993)). Ribavirin (1-xcex2-D-ribofuranosyl-1,2,4-triazole-3-carboxamide) is a synthetic guanosine analog that has been used to inhibit RNA and DNA virus replication. (Huffman et al., Antimicrob. Agents. Chemother., 3:235 (1973); Sidwell et al., Science, 177:705 (1972)). Ribavirin has been shown to be a competitive inhibitor of inositol mono-phosphate (IMP) dehydrogenase (IMPDH), which converts IMP to IMX (which is then converted to GMP). De Clercq, Anti viral Agents: characteristic activity spectrum depending on the molecular target with which they interact, Academic press, Inc., New York N.Y., pp. 1-55 (1993). Intracellular pools of GTP become depleted as a result of long term Ribavirin treatment.
In addition to antiviral activity, investigators have observed that a few guanosine analogs have an effect on the immune system. (U.S. Pat. Nos. 6,063,772 and 4,950,647). Ribavirin has been shown to inhibit functional humoral immune responses (Peavy et al., J. Immunol., 126:861-864 (1981); Powers et al., Antimicrob. Agents. Chemother., 22:108-114 (1982)) and IgE-mediated modulation of mast cell secretion. (Marquardt et al., J. Pharmacol. Exp. Therapeutics, 240:145-149 (1987)). Some investigators report that a daily oral therapy of Ribavirin has an immune modulating effect on humans and mice. (Hultgren et al., J. Gen. Virol., 79:2381-2391 (1998) and Cramp et al., Gastron. Enterol., 118:346-355 (2000)). Nevertheless, the current understanding of the effects of Ribavirin on the immune system is in its infancy.
It has been discovered that Ribavirin can be used as an adjuvant to enhance an immune response to an antigen. Embodiments described herein include xe2x80x9cstrongxe2x80x9d vaccine preparations that comprise an antigen and Ribavirin. Generally, these preparations have an amount of Ribavirin that is sufficient to enhance an immune response to the antigen. Other aspects of the invention include methods of enhancing the immune response of an animal, including a human, to an antigen. By one approach, for example, an animal in need of a potent immune response to an antigen is identified and then is provided an amount of Ribavirin together with the antigen that is effective to enhance an immune response in the animal. In some methods, the Ribavirin and the antigen are provided in combination and in others, the Ribavirin and the antigen are provided separately. Thus, several embodiments concern the manufacture and use of vaccine preparations having Ribavirin and an antigen.
Preferred vaccine compositions comprise Ribavirin and a hepatitis viral antigen. The antigen can be a peptide or nucleic acid-based (e.g., a RNA encoding a peptide antigen or a construct that expresses a peptide antigen when introduced to a subject). HBV antigens that are suitable include, for example, hepatitis B surface antigen (HBsAg), hepatitis core antigen (HBcAg), hepatitis e antigen (HBeAg), and nucleic acids encoding these molecules. Compositions having Ribavirin and an antigen from the hepatitis A virus (HAV) or Ribavirin and a nucleic acid encoding an antigen from HAV are also embodiments. Still further, compositions having Ribavirin and an antigen from the hepatitis C virus (HCV) or Ribavirin and a nucleic acid encoding an antigen from HCV are embodiments.
Furthermore, compositions having a mixture of the antigens above are embodiments of the present invention. For example, some compositions comprise a HBV antigen, a HAV antigen, and Ribavirin or a HBV antigen, a HCV antigen, and Ribavirin or a HAV antigen, a HCV antigen, and Ribavirin or a HBV antigen, a HAV antigen, a HCV antigen, and Ribavirin. Other embodiments comprise Ribavirin and a nucleic acid encoding a mixture of the antigens described above. Some embodiments also include other adjuvants, binders, emulsifiers, carriers, and fillers, as known in the art, including, but not limited to, alum, oil, and other compounds that enhance an immune response.
Preferred methods involve providing an animal in need with a sufficient amount of Ribavirin and a hepatitis viral antigen (e.g., HBV antigen, HAV antigen, HCV antigen a nucleic acid encoding one of these antigens or any combination thereof). Accordingly, one embodiment includes identifying an animal in need of an enhanced immune response to a hepatitis viral antigen (e.g., an animal at risk or already infected with a hepatitis infection) and providing to said animal an amount of Ribavirin that is effective to enhance an immune response to the hepatitis viral antigen.